This invention relates to a technique for measuring the derivatives of device parameters and, more particularly to measuring the first and second derivatives of the light-current-voltage characteristics of AlGaAs double heterostructure junction lasers.
Derivative techniques are employed in many fields of science and engineering. Reasons for their use range from the enhancement of signal-to-noise ratio, as in nuclear magnetic resonance and optical reflectivity investigations of band structure, to the convenience of direct measurement of dynamic transistor characteristics. Usually the techniques measure system response to a small ac modulation, often using phase detection for signal enhancement.
These techniques have recently been successfully applied to an analysis of the current-voltage characteristics of GaAs injection lasers. The first derivative dV/di has been shown to be useful, both in homojunction and in double heterostructure lasers, for measuring the parameters entering the i-V characteristic as well as for extracting lasing threshold and other features intimately related to the lasing process.